The tetrapeptide H-thr-pro-arg-lys-OH (TPAL) acts to prevent maturation of follicles and is a pre-ovulatory contraceptive compound. The tetrapeptide H-thr-arg-lys-arg-OH (TALA)may compete with TPAL for binding site on the plasma carrier protein and thus act as a post-coital contraceptive compound but, at least, TALA does prevent TPAL action and does enhance ovulation. The steroid from oviductal stroma is definitely a post-coital contraceptive compound. The attack on the problem will involve (1) isolation of more plasma carrier protein for binding analyses. (2) Use tagged TPAL for site of action study and (3) see if TPAL and TALA compete for site (RIA study). (4) Make tagged TPAL. (5) If TPAL acts at hypothalamus or pituitary see if active in males as contraceptive. (6) Size of embryonic storage protein and (7) size of same after TPAL is removed. (8) Isolate steroid from oviducts and (9) do preliminary analyses of steroid structure. (10) Test Diamalt TPAL on E2 and P levels in hamsters and (11) see if Diamalt TPAL works orally. (12) FSH and LH analyses if TPAL works in higher centers and (13) check E2 and P levels in rats after TPAL injections sc.